Traditionally, dry colors, which are powdery coloring compositions comprising a mixture of a dye or a pigment and a dispersing agent, liquid colors or paste colors, which are coloring compositions comprising a pigment dispersed in a dispersing agent that is liquid at ordinary temperatures, master batches, which are pellet-like, flake-like or bead-like coloring compositions comprising a pigment dispersed in a resin that is solid at ordinary temperatures, and the like, are used to impart colors to thermoplastic synthetic resins. These coloring compositions are used for various purposes making use of the features thereof.
Of these compositions, dry colors comprise a simple mixture of powders of a dye or a pigment and an additive (e.g., metal soaps, waxes, etc.) and are generally inexpensive, but are slightly problematic in terms of dispersibility in synthetic resins, and also problematic in that they are likely to scatter because of the fine powder state during use.
Preferably used for the sake of ease of handling and workplace environmental conservation during use are master batches. Master batches are required to have high dye or pigment concentrations, to minimally affect the various physical properties of thermoplastic resins to be colored, such as heat resistance and mechanical strength, and there have recently been increased demands for better pigment dispersibility and partition quality with the increases in molding precision and speed for thermoplastic resins to be colored.
Furthermore, traditionally, resin parts have been joined together by fastening with fastening parts (bolts, screws, clips, etc.), adhesion using adhesives, vibration welding, ultrasonic welding, and the like. According to laser welding, secure welding is achieved by simple operation to provide strength equivalent to or more than the levels expected by conventional welding, and in addition labor saving, productivity improvements, production cost reductions, etc. can be achieved because vibration and heat have minimal effects. With these features, laser welding is suitable for the joining of functional components, electronic components, etc., for which the avoidance of the influence of vibration and heat is desired in, for example, automobile industry, electric/electronic industry and other fields, and is applicable to the joining of resin parts of complex shapes.
Laser welding of synthetic resin materials can, for example, be conducted as described below. As shown in FIG. 3, one member incorporating a laser ray transmitting material and another member incorporating a laser ray absorbing material are brought into contact with each other. When irradiating laser from the laser ray transmitting material side to the laser ray absorbing material, the laser ray that has penetrated the laser ray transmitting material is absorbed in the laser ray absorbing material and generates heat. By this heat, the laser ray absorbing material is molten around the portion that has absorbed the laser, and the laser ray transmitting material is also molten, the resins of the two members fuse together, and upon cooling sufficient welding strength is obtained and the laser ray transmitting material and the laser ray absorbing material are joined firmly. Features of laser welding include the capability of welding without bringing the laser generation portion in contact with the portion to be welded, the minimal thermal effect on the surrounding portion because the heating is localized, freedom from the problem of mechanical vibration, the capability of welding of fine portions and structures, high reproducibility, maintenance of high air-tightness, high welding strength, inconspicuous welded portion, and no generation of dust etc.
As a technology concerning laser welding, Japanese Patent Laid-Open No. HEI-11-170371 (patent document 1) describes a method of laser welding comprising a step wherein laser ray is irradiated so that it focuses on a portion where an opaque member comprising a laser ray absorbing thermoplastic synthetic resin and a colorless transparent member comprising a laser ray transmitting thermoplastic synthetic resin are in contact with each other. In this case, however, when viewed from the colorless transparent member side, the welded portion differs from the non-welded portion in color and smoothness, posing a problem of poor appearance.
Of such dyes/pigments used to impart colors to molding resins, yellow ones having a structure such as of the azo, anthraquinone, quinophthalone, or metal complex are currently used.
For example, Japanese Patent Laid-Open No. 2000-309694 (patent document 2) discloses a resin composition incorporating a black colorant formulated with Sandoplast Yellow and Sandoplast Violet. However, because the quinophthalone yellow colorant used therein, i.e., C.I. Solvent Yellow 114, is exposed to high temperature for a long time in cases of long resin melting time, such as resin molding using a large molding machine, decomposed dyes/pigments can contaminate not only the resin, but also various portions of the molding machine and other equipment.
Dyes/pigments for coloring resins, especially those for coloring high-melting plastics, pose a considerable problem of color fading due to exposure to high temperature during resin molding. In the above-described method of laser welding as well, colorant heat resistance is an important factor.
If the molded product is exposed to high-temperature high-humidity conditions, dye fastness, such as anti-migration property, is also of concern under the high-temperature high-humidity conditions.
Therefore, there has been a strong demand for a structurally highly stable yellow colorant for coloring recently developed high-melting engineering polymers.
However, with conventional yellow dyes/pigments for coloring resins, it has been very difficult to meet all requirements of fastness, such as heat resistance, moisture resistance, solvent resistance, and anti-sublimation property, while meeting the requirements for brilliant color impartment and uniform compatibility or dispersibility to resins.
Patent document 1: Japanese Patent Laid-Open No. HEI-11-170371
Patent document 2: Japanese Patent Laid-Open No. 2000-309694